A lot of it is unquantifiable physics. You're trying to get the wavelength so it matures right at the microphone.

-- Troy Irving, extreme sound system owner

(Popular Science) --Troy Irving's 18-year-old Dodge Caravan has a heck of a sound system: 72 amplifiers -- you got it, 72 -- and 36 big 16-volt batteries to put out the 130,000 watts of power needed to rumble his nine 15-inch subwoofers.

To put that into perspective, the most powerful production-car audio I know of is the $230,000+ 2003 Aston Martin Vanquish's 1,200-watt system. Irving carries $80,000 worth of audio alone, in a vehicle that is worth, admittedly, slightly less than the Maybach. Must be fun to ride down Main Street with the windows rolled down, right?

Not really. At a curb weight of about 10,000 pounds, the Caravan is basically undrivable. There is virtually no room for a driver, and even less for a passenger.

"We need more batteries, but that's all the room we have," Irving gripes. But he can at least sit in his driveway and listen to music, yes? Actually, no. Irving's audio system can't play music. It's designed to play a single frequency -- 74 Hz -- very loud. Irving, you see, is a dB drag racer.

Growing sport

dB (as in decibel) drag racing is an obscure but growing international "sport" in which competitors go head-to-head for two or three seconds at a time -- hence the name drag racing -- to establish whose sound system is loudest. The 2002 record, set by a German team of secretive audio engineers, was 177.6 dB.

The roar of a 747 on takeoff is usually quantified at about 140 decibels, although there's really no way to correlate the wide-spectrum noise of jet engines in open air with a low-frequency pure tone inside a highly reflective enclosure. Because the decibel scale is logarithmic, with every 10 dB increase equivalent to a doubling of perceived sound (otherwise known as noise), dB drag racing enthusiasts create some seriously loud tones. (Another rule of thumb: All else being equal, every three dB of increased sound from a typical dB drag racing system requires a doubling of amplifier power.)

Bolting doors shut

Such noise would turn your brain to tofu if it weren't generated into uninhabited, tightly sealed space, such as the interior of a vintage Caravan. Competitors in the Extreme class bolt doors shut. Irving uses industrial jig clamps and a threaded one-inch steel rod and nut through the window for extra security. Drag racers replace windows and windshields with Plexiglas up to two inches thick, secure panels with turnbuckles fit for an America's Cup racer and, in some cases, fill the doors with concrete. Then, while the tone burst is generated, team members lie spread-eagled on the roof and push against the car from the outside to bolster it that little extra bit. One Extreme competitor in search of ultimate stiffness used an armored truck, so we can expect to see Iraq-campaign M1A1 Abrams tanks doing sonic smoky burnouts as soon as they're declared surplus.

The sound that leaks out is pretty much what you hear when you inadvertently turn your home stereo on with the volume all the way up and a loose speaker wire: a rattling, destructive, marrow-fluttering hum.

Speakers run like engines

Literally destructive. Many teams spend the time between runs repairing blown speaker cones, which is the dB drag racing equivalent of John Force's melted pistons.

"These speakers are like funny-car engines," Irving says. "Some of those cars run for three or four seconds. That's what we design these for -- very short bursts of extreme power. Run them down the road for 30 minutes playing music and they'll be useless." At the volumes dB racers run, speaker voice coil temperatures spike almost instantly, going as high as 500°F, and the sound deteriorates.

At the end of each major meet, the four loudest competitors line up for the "deathmatch," a five-minute, winner-take-all face-off in which they fire sound salvos at one another as judiciously yet loudly as possible, trying to keep their speakers and power sources alive until time is up. Amid the reek of ozone and melting metal, often just one is left standing. Only heavily sponsored competitors dare play this last game, since the cost in equipment is so high.

Sound trumps looks

Many of the cars that performed at a dB drag racing event I attended in Toronto were sad-looking beaters, some with zoomy but faded paint jobs advertising their sponsors or owner's car-audio shop. A Super Street class Nissan Pulsar brush-painted a bilious green putted onto the judging ramp, driven by a kid sitting on a plastic milk crate.

A jumble of amps, cables and batteries was barely visible through the dirty back window. Yet it blew away its bracket partner with a thunderous 158.2. "Cosmetics aren't going to make it any louder," says Extreme competitor Frankie Valenti.

Valenti was frazzled, having pulled an all-nighter trying to get his GMC van's "enclosure" right. The efficacy of the whole system is largely determined by the sharp-edged, multi-faceted shape inside the van -- usually built of wood as much as 4 inches thick -- with fiberglass covering what used to be the dashboard, center console, steering column and anything else the builder figures will decrease internal volume; the point is to direct as much sound as possible at the judges' in-car microphone.

Noise by trial and error

The enclosure shapes are as goofy and angular as a stealth fighter's. Some work, some don't. "It's just guesswork," Irving admits. "You start with one thing and if it works, you make the airspace smaller. If that works, you make it smaller again."

Says Valenti: "We could move one piece and the level might go up 10 dB, but it takes a lot of time and work. I could be sitting on a number higher than anybody, if I move that back wall forward a foot."

Valenti admits he's often asked why he pursues this hugely pointless hobby. "Yeah, it's weird. But there are people who have tens of thousands of dollars invested in stamp collections, for God's sake. That to me is weird."

As Troy Irving's partner, Jason Bradley, explains, "You start out with a nice stereo in your everyday car, and it grows and grows and eventually gets out of control. The sad thing is, I don't even have a stereo in my daily driver anymore," he says, laughing. "Every dime I have goes into this equipment."

Hundreds of events expected

How does a sport like this do in tough economic times? Just fine. There are 465 events listed in the current season. "Our competitors can't even spell recession," says dB drag racing impresario Wayne Harris. "They're young, and some of them still live at home. They put all their energy and money into their cars. They're competitive. They're at that age."

Most of the teams wear sponsor-bedecked uniforms and have race-painted and decaled cars. "Pit crews" of six or eight suited-up mulletheads often tend to the cars. So it came as a shock when Jason Parsons drove onto the ramp in his clean, stock, unmarked '87 Impala and all by himself threw down a 155.8 to win his category in the Super Street class. "Yeah, I play music through the system," he tells me. "Be silly not to." What a good idea. Does he have any interest in moving up to the Extreme classes? "No, they're out after world records. That and tax write-offs for their audio shops."